CFD-Based Hydraulic Performance Improvement of a Chlorine Contact Tank: The Case Study of a Southern Italy Plant

Chlorine contact tanks are crucial for wastewater disinfection, with performance strongly influenced by internal hydraulic characteristics. This study applies Computational Fluid Dynamics (CFD) to analyze and improve the hydraulics of the chlorination contact tank in a Wastewater Treatment Plant in the Southern Italy. A three-dimensional transient CFD model was developed using the Reynolds-Averaged Navier–Stokes (RANS) equations with the Renormalized Group (RNG) turbulence closure. The model simulated flow patterns, tracer transport, and chlorine decay kinetics under the existing configuration and two alternative configurations. Conservative tracer pulse simulations enabled the calculation of Residence Time Distributions (RTDs) and hydraulic efficiency indicators, including the Baffling Factor (θ10), Morrill index (Mo), and Aral–Demirel index (AD). A typical contact tanks geometry exhibits specific hydraulic characteristics, including recirculation behind baffles and stagnant zones in sharp corners, which inevitably affects the contact time. The first alternative, namely featuring rounded corners, moderately reduced dead zones, but did not substantially mitigate recirculation. The second alternative, herein called combining rounded corners with perforated baffle walls, substantially improved hydraulic performance, yielding flow patterns closer to plug-flow. RTD peaks were higher and narrower for the modified designs, and hydraulic indices improved, with Mo decreasing by approximately 5%. These hydraulic enhancements are expected to increase disinfection efficiency by providing more uniform chlorine exposure. The results demonstrate that geometric modifications effectively optimize contact tank hydraulics and highlight the role of CFD as a design and retrofit tool for water and wastewater disinfection systems.